Fresh Air Ventilation

By today’s standards, the Type 4’s heating and ventilation system isn’t good but, for a vehicle originally designed in the late 1960s, it was pretty advanced. The best feature so far as I am concerned is that you can get warm (or even hot) air to your feet and hands and cool air to your face at the same time ... a feature that is impossible in many cars today.

The output from the Eberspächer petrol heater is blown into the car’s interior by a fan in the engine compartment and is distributed to all open vents. However, fan assistance for fresh air is only available to the vents to the windscreen and the side windows. The fresh air to the main vents in the centre of the dashboard depends on the forward motion of the vehicle. So when stuck in traffic on a hot summer’s day, you have no fresh air apart from that wafting in through the open windows.

I thought I could improve things. I wanted to enable the dashboard vent slider to activate the fan so that I can have fresh air blown into the interior when stationary without diverting precious air to the windscreen. There were two parts to this job, firstly to modify the switch frame to take a second contact strip and, secondly, to convert a spare contact strip to switch on at the opposite end.

This is the slider switch frame with the two sliders out of the car viewed from the underside. The pegs that connect with the cables that operate the flaps are out of sight here. The slider on the left in this view operates the mixer vents and the contact strip is visible behind it.
Here is the frame after the sliders and contact strip have been removed.
Here I have welded in a piece cut from another frame to give me the mounting holes I need for the second contact strip.
I added a couple of in-fill pieces to strengthen the points and to make it look neater. It will look even better after recoating.
On the left here is a standard contact strip and, on the right, one with the two parts separated and the vertical part reversed. The two square brass contacts can just about be made out.
I considered all sorts of fancy methods and solvents to weld the two pieces back together again but decided to try my hot-melt glue gun. The result can be seen here. I reassembled the mechanism and went on to my next job but after a week I found that the modified contact strip had yielded to the pressure of the slider. The hot-melt hadn’t fused properly into both parts. I cleaned it up and tried some solvent cement designed to glue plastic drain pipes together. This seemed much stronger and held firm for more than a year before the parts separated again and I was back to square one!
I realised that my mistake had been to cut the contact strip on the assumption that I could fix the two parts back together. I decided to start again with a new contact strip and move the contacts. I carefully removed the two brass contacts and reinserted them in their new position by heating them with my Weller soldering gun and pushing them through the melting plastic. I needed to fill the two holes left by the original contacts to provide a smooth surface for the slider and I cut a couple of strips of stainless steel as shown here which I bent round the back to secure them.
Here is the complete kit of parts ready for reassembly. I have cleaned up the frame and resprayed it to resemble the original colouring as closely as I could.
Here is a top view of the mechanism reassembled with both sliders in the closed position.
From the other side the terminals on the two contact strips can clearly be seen. All I have to do is to parallel the respective terminals and I shall have a two-speed fan available independently for cabin and windscreen vents.